Surface blowing process for making steel



Aug. 18, 1959 w. l.. KERLIE SURFACE BLowING PRocEss FOR MAKING STEEL 2Sheets-Sheet l Filed June l, 1956 /N VEA/TOR.'

WALTER Lj/fERL/E, er: @mba Adri /'s Attorney.

w. I .KERLIE SURFACE BLOWING PROCESSl FOR MAKING STEEL 2 Sheets-Sheet 2Filed June l, 1956 //V VE /V TOR.'

E, E H K. R L, ,W n vl. B

Patented Aug'. 18, 1959 SURFACE BLOWING PROCESS FOR MAKING STEEL WalterL. Kerlie, Monroeville, Pa., assigner to United States SteelCorporation, a corporation of New Jersey Application June 1, 1956,Serial No. 588,762

6 Claims. (Cl. 75-60) l This invention relates to a pneumatic processfor refining pig iron which utilizes surface blowing as distinguishedfrom submerged blowing wherein the blast is introduced below the surfaceof the metal as in bottom-blown and side-blown conventional Bessemerconverter practices. More particularly, it relates to the surfaceblowing process disclosed in United States Patent No. 2,733,141 toClarence E. Sims and is concerned with improvements in such processwhich are directed to the end of obtaining a more ecient refiningoperation and to the solution of incidental problems which determine thepracticability of the process. Among other features, the process of thisinvention reduces iron losses and increases the life of the converterrefractory lining by controlling the circulating movement of the slagover the molten metal and by causing the gases to ow spirally throughthe converter.

Prior to development of the surface blowing process disclosed in theabove mentioned Sims patent, pneumatic processes for refining steel wereuniversally regarded in the steel industry as being unsuitable formaking deep drawing low carbon steels and as havinglrestrictedapplication to certain types of pig iron. With respect to pig ironcomposition, the acid Bessemer process requires a pig iron high insilicon (1.0% min.) and low in phosphorus (0.10% max.), and the basicBessemer process requires a pig iron with a silicon content less than1.0% and high in phosphorus (1.3% min.). Low carbon steels having gooddeep drawing characteristics cannot be produced by these processesbecause the blow required for lowering the carbon content resultsinpexcessive absorpftion of nitrogen. As a consequence, the slower andmore expensive open hearth practice has Ibeen considered essential formaking steels which are low in carbon, phosphorus and nitrogen as wellas for rening American basic pig iron which has a phosphorus content inthe range of 0.15% to 0.5% and is thus unsuitable for Bessemeroperations.

Contrary to these viewpoints, the Sims process proposes to refineAmerican basic pigriron and to produce steel which is low in carbon,phosphorus vand nitrogen by a pneumatic surface .blowing operation. Asdisclosedl and explainedin the abovermentioned patent, it is essentialto this process that a rolling state of agitation of the slag on thesurface of the metal be produced by the air blastf, For this purpose,the patent specifies among other requirements a blast delivering air ata low angle ofv incidence against the surface of the bath, at a velocityof .300 to 500 feet per second, and at a rate which will -remove aboutV0.5 carbon per minute, to maintain the condition of slag agitationessential to a successful refining operation. The latter involves theintroduction of air at ratesy as high as 1500 c.f.m. per ton of ironcharged. Since the improvementsofvthis invention relate to andcontemplate a practice of the Sims surface blowing procless, referenceis accordingly made to the above mentioned United States Patent No.2,733,141 for a more detailed description and further understanding ofthe features of the process which are used in the practice of theimprovements of this invention.

In general, the air required in the Sims surface blowing process entersthe vessel at about room temperature and is heated almostinstantaneously by the oxidation reactions it causes, to a temperatureof about 2500" F. expanding to some twenty times its original volume. Asa result, the different gases leave the vessel at a velocity which isconducive to iron and slag losses by ejection from the converter mouthwhich, in the converter shown in the above mentioned Sims patent as wellas in most conventional converters, is located directly over the moltenbath. In accordancewith the principles of this invention, slag and ironlosses of this nature and splashing tendencies are reduced by conductingthe blowing operation in a converter which has its mouth located at oneside of the bath and thus provides a cover over the bath. The provisionof a bath cover in this manner prevents the movement of splashing slagand metal directly outl of the converter mouth with the burning gas asis permitted in conventionally constructed converters. As an incident topreventing slag and iron losses by splashing in this manner, a spiralmovement is imparted to the gases during movement to the converter mouthwhich produces an improved heat transfer to the bath by effecting morecomplete combustion of carbon to CO2. This increased heat is availableto melt scrap and thus increases the yield of the operation.

The Sims process further produces an extremely fluid slag which, in viewof the blast velocities required to maintain it in the rolling state ofagitation essential to this process and the enormous increase in gasvolume which occurs adjacent to the discharge ends of the tuyeres,results in a surging condition of the slag cover on the bath. Thissurging condition causes damage to the refractory lining of theconverter vessel, the tuyere blocks in particular, when conducted in avessel of the conventional design shown in the said patent. As shown inthe patent, the blast is applied to the surface of the bath at a lowangle of incidence from one side of the vessel and, in practice, thishas been found to throw a surging non-circulating wall of slag againstthe other side of the vessel which in rolling lback toward the tuyeresenvelops the blast and is violently hurled by the expandinggases againstthe refractory lining. The resulting eroding or wearing action on thevessel lining is particularly bad in the tuyere wall area since it cutsthis wall unevenly and rapidly increases the distance of the tuyeresfrom the bath. The latter is conducive to surging and the wear thusproceeds at an increased rate. The improvements of this inventioneliminate this condition by giving-the bath a particular shape andprojecting the Vblast against its surface in such manner that the slagand Vtion about a horizontal axis and has -rounded ends and a mouth ornose portion opening out Vof one of such ends. The provision of a vesselof this shape enables a more shallow bath to be had with a greatertuyere blast area per ton of metal. The vessel shape and tuyere blastcooperate to provide the continuous circulating movement ofthe slag overthe surface of the metal. p y

Further details4 and advantages of the invention will become apparentfrom the following description. In the drawings, there is shown apreferred form of apparatus for practicing the improved process of thisinvention. In this showing:

Figure 1 is a side elevation of a converter which is particularlyadapted to the practice of the process of this invention;

Figure 2 is a Vertical sectional View taken substantially inthe plane ofthe line II-II of Figure l;

Figure 3 is a sectional View taken substantially in the plane of theline III-III of Figure 2;

Figure 4 is a sectional view taken substantially in the plane of theline IV-*IV of Figure 2; and

Figure 5 is an enlarged and detailed sectional view of one end of theconverter vessel which shows its connection to an air blast coupling.

As stated above, the practice of the process of this invention iseffected in a converter vessel which has its mouth or nose positioned atone side of the bath and thus provides a cover over the bath. Apreferred form of vessel for this purpose is designated as a whole bythe numeral 1 in the drawings which show it as having a cylind-rical orbarrel shape. It has a metal shell 2 with a refractory lining 3 in themanner of conventionally fabricated converters and is mounted forrotation with its axis in a horizontal position. Its mounting includes apair of axially spaced rocker rails or wheels 4 which are secured to theshell 2 concentrically with respect to the axis of the vessel 1 and haverolling engagement on supporting rollers 5. A sprocket or gear drive(not shown) is provided for tilting the vessel 1 to and from its uprightblowing position as shown in the drawings. i

As best shown in Figure 5, the inner end of the vessel 1 is closed by amanhole cover which includes a mounting plate 6 and a prerammed andtapered dolomite block l7. Wedge and cotter assemblies 8 secure theplate 6 to the shell 2 as in the standard basic Bessemer converter. Theprovision of a removable manhole in this manner enables replacement ofthe refractory lining 3 according to the practice used in reliningstandard basic Bessemer converters. For relining in this manner, themanhole 6 is removed and the vessel 1 is placed in an upright positionafter removal from its supporting rollers 5. After the lining 3 has beenreplaced, a tape-red block 7 is rammed into position and the wedgingcotters 8 are operated to secure the plate 6 to the shell 2.

A wind box 10 extends between the rocker wheels 4 and is supplied withair from a coupling 11 which is connected with the wind box 10 by aconduit 12. The cou- -pling 11 is removably secured to the shell 2 aboutthe manhole plate 6 and is `connected to an air supply conduit 13 whichis rotatably supported in a bearing 14.

At its outer end the converter has a nose section 15 which is shaped toprovide a mouth 16 in a skewed and eccentric position with respect tothe axis of the converter as best shown in Figure 3. When the vessel isin its operative blowing position as shown in the drawings, its mouth 16is arranged at one side of the areardirectly over the bath and facesoutwardly in an endwise direction from the vessel. The mouth 16 has itslower edge -17 located well above the surface 18 of the converter bathand its upper edge 19 is flush with the top 20 ofthe lining whichprovides a cover over the bath. From the lower edge 17, the liningsurface 21 slopes downwardly at an angle of approximately 45. The shapeof the nose 15 and the skewed location of the mouth 16 are effective inpreventing ejection of metal and slag from the vessel by splashing. Totap slag or metal it is only necessary to rotate the vessel in acounter-clockwise direction as viewed in Figure 2 to lower the mouth 16to a position below the level of a bath in the converter. The mouth 16preferably has a large diameter providing for visual inspection of thelining and such fettling `repairs thereto as may be needed. Thelprovision of a wide zmouth 16 in a relatively short nose section15,resu1ts in ,a relatively low velocity of the spirally moving wastegas emerging from the vessel. In this manner, deposition of slag andmetal in the upper portion of the nose 15 is kept at a minimum andskulling of the mouth 16 is eliminated.

The wind box 10 mentioned above delivers air to a plurality of tuyeres25 in a preformed refractory block 26 which is rammed in an opening inthe lining 3 as best shown in Figure 2. The tuyeres 25 are parallel andextend transversely of the vessel axis so that the gases have a spiralmotion in moving to the mouth 16. The block 26 is held in position by abottom plate 27 secu-red to the shell 2. The plate 27 has openings 29through which air is delivered from the wind box 10 to the tuyeres 25.Upper and lower edges of the box 10 are formed by side plates 30 whichare b olted to the shell 2 and at their ends to the rocker rails 4. Acover plate 31 completes the enclosure for the wind box 10 and isprovided with sight openings 32 so that furnace conditions may beobserved by sighting down the tuyeres 25.

Figure 2 shows the angular positions of the tuyeres 25 when theconverter is in an operative blowing position. In this position, thelower ends 33 of the tuyeres 25 are positioned above (one to seveninches in practice) the surface 34 of the metal and preferably slightlyabove the surface 35 of the slag, which surfaces are designated by thebroken lines in Figures 2 and 3. The axes of the tuyeres 25 respectivelyform a at angle of incidence with the surface of the metal which shouldbe kept be;- tween 10 and 20. For best surface blowing conditions, thisangle should be about 15. The tuyere axes intersect with a verticalplane through the center of the mouth 16 at an angle of less than andwhich is 75 for the preferred tuyere angle of 15 As shown in Figure 2,the main body of the vessel 1 is eccentrically disposed with respect tothe rocker wheels 4 so that, for any given size of unit, the maximumdistance between the tuyeres 25 and the opposite wall 37 of the lining 3obtains. In this way erosion of the wall 37 opposite the tuyeres isreduced to a minimum. Furthermore, the thickness of the opposite wall 37can be increased, if necessary, to match the wear on other parts of thevessel lining and, consequently, to improve the overall lining life ofthe Vessel. The eccentric disposition of the vessel 1 with respect tothe rocker wheels 4 further permits the use olf a relatively largediameter vessel and still leaves sufficient space for the blast box 10Within the perirneters of the rocker wheels 4.

The main body of the vessel 1 has a curved or barrel shape as shown in|Figure 3 and has its ends rounded in the regions 38 and 39 (see Figure3), In addition, the side wall of the vessel is flattened in the region40 (sere Figure 2) above the tuyere block 26 so that the bath containedin the vessel will have a substantially D-shaped surface contour withthe tuyeres 25 arranged along the flat side of the D-shape. In operationthe air blast from the tuyeres 25 molves the slag across the surface ofthe metal toward the opposite wall 37. However, and by reason of thecurvature of the wall 37 in a horizontal plane, the slag will not buildup against such wall but will circulate continuously in two distinctzones, one at each end of -the vessel, over the surface of the metal asindicated by the arrows in Figure 4. This circulating movement orf theslag gives rise to more intimate mixing with the metal as well as a morerapid uxing of the Vslag forming materials because the FeO formed by theits axis horizontal and'mounted for rotation about such axis ispreferred-for the reason that it provides a more shallow bath whichgives a greater tuyere area perton of metal in addition to providing forcirculation 'of the slag overthe surface of the metal; In addition, thearrangement of the 'vessel 1 on its side V with its lmouth 16 at; oneend provides a cover over the entire surface ofthe bath. This furtherreduces losses by splashing and spraying which are otherwise apt to takeplace in a converter having its mouth open to the atmosphere in an areadirectly over the bath.

The gases produced by the blast from the tuyeres 25 adopt a spiralmotion in moving toward the mouth 16. This spiral motion is the resultof a rotational movement caused by the curvature of the wall 37 oppositethe tuyeres 25 and the axial movement of the gases toward the mouth 16.The spiral movement results in a better mixing of the gases and morecomplete combustion of carbon to carbon dioxide within the vessel and animproved heat transfer to the bath. This gives rise to additional heatsuflicient to melt an appreciable quantity of scrap and increases theproduction of the converter.

From the standpoint of reducing splashing, improved slag circulationwith respect to elimination of the surging slag wall mentioned above,and imparting a spiral motion to the burning gases, best results areobtained when the spacing between adjacent tuyeres 25 is maintainedwithin limits determined by the tuyere diameters and the wind velocityin the tuyeres. The minimum tuyere spacing is given by the empiricalequation wherein S is the tuyere spacing in inches, D is the tuyerediameter in inches, and V is the wind velocity in feet per second. Ithas also been found that there is little advantage in making the tuyerespacing greater than 3.0 DWZ/l06 inches. For example, with five 5inchtuyeres and a wind velocity of 500 feet per second, the tuyere spacingshould be between 16 and 19 inches; with three 61/z-inch tuyeres and thesame wind velocity, the tuyere spacing should be between 26 and 32inches.

To obtain most effective slag circulation, the axial length of theside-circulation zones (as measured by the distance between the centerline of the outer tuyeres and the ends of the bath) should be 27-l-S/2inches to achieve an adequate return circulation and thereby an adequatemixing of metal and slag-forming constituents. For example, with fiveinch tuyeres and a wind velocity of 500 feet per second, the width ofeach side-circulation zone should be at least 35 inches, and the lengthof the bath should be at least 134 inches. The spacing of the outertuyeres from the ends of the bath results in the application of theblast to an area centrally of the bath so that the slag is circulatedover the circular paths as designated by the arrows in Figure 4.

In operation of the converter, the lime required for a charge is addedto the vessel which is then rotated to place the tuyere ends 33 abovethe expected level of the bath. After charging molten pig iron bypouring through the mouth 16, the vessel is rotated to lower the tuyeresto their blowing position. The blast is then turned on and the blowingproceeds. Attention is particularly directed to the fact that thecylindrical shape and horizontal position of the vessel 1 provides acover over the bath during blowing. Since the tuyeres 25 project theblast against the surface of the bath in a direction transversely of thevessel axis, splashing slag and metal s not carried out of the vesselbut is projected against the bath cover provided thereby. Thistransverse direction of blast relative to the axis of the vesseltogether with the curvature of the vessel wall 37 and the arrangement ofthe mouth 16 at one end of the vessel cause a spiral movement of thegases to the mouth 16 as explained above. Attention is further directedto the fact that this transverse direction of blast in cooperation withthe shape of the bath is eectiveY in circulating the slag and metal overthe surface of the bath for the reasons mentioned above.

While one embodiment off my invention has been shown and described itwill be apparenty that other adaptations and modifications may bemadewithout departing from the scope of the following claims. j

.Ici-nm: E "'1. Ay pneumaticfprocess for rening'iron which comprisescharging a bath of molten iron and slag in'a converter, projecting anoxidizing blast at a low angle of incidence against the surface of saidbath in a direction across an area of said surface arranged centrallybetween surface areas at the ends thereof, utilizing said blast to moveslag over said central area, and circulating the slag in oppositerotational directions over the said end areas of said bath to return itinto the path of said blast.

2. A pneumatic process for refining iron in an elongated converter whichcomprises supporting said converter in a horizontal position, charging abath of molten iron and slag in the lower portion of said converter,projecting an oxidizing blast at a low angle of incidence against thesurface of said bath in a direction transversely of said converter andacross an area of said surface arranged centrally between surface areasat the ends thereof, utilizing said blast to move slag continuously oversaid central area, and circulating the slag in opposite rotationaldirections over the said end areas of said bath to return it into thepath of said blast.

3. The pneumatic process defined in claim 2 characterized by projectingsaid blast from a plurality of tuyeres arranged at spaced intervalsalong and extending radially through a side portion of said converteropposite said bath central area.

4. A pneumatic process for reiining iron in a converter having a gasdischarge mouth at one end thereof which comprises supporting saidconverter in a horizontal position with its said gas discharge mouthopening outwardly therefrom, charging a bath of molten iron and slag inthe lower portion of said converter, projecting an oxidizing blast at alow angle of incidence against the surface of said bath in a directiontransversely of said converter and across an area of said surfacearranged centrally between surface areas at the ends thereof, utilizingsaid blast to move slag continuously over said central area, circulatingthe slag in opposite rotational directions over the said end areas ofsaid bath to return it into the path of said blast, and moving the gasesproduced by said Iblast with a spiral motion over the surface of saidbath to said converter gas discharge mouth. v

5. In a pneumatic process for refining iron in a converter the lowerportion of which has a D-shaped contour in a horizontal plane, the stepswhich comprise charging a bath of molten iron and slag in said lowerportion, projecting an oxidizing blast at a low angle of incidenceagainst the surface of said bath in a direction from the iiat side ofthe converter toward the curved side thereof and across an area of saidsurface arranged centrally between surface areas at the ends thereof,utilizing said blast to move slag continuously over said central area,and circulating the slag in opposite rotational directions over the endsof said curved side and the said end areas of said bath to return itinto the path of said blast.

6. In a pneumatic process for refining iron in a converter supported ina horizontal position with its mouth opening axially outwardly from oneend thereof, said converter having a barrel shape with a iiattenedportion along one side thereof such that its lower portion has aD-shaped contour in a horizontal plane, the steps which comprisecharging a bath of molten iron and slag in said lower portion,projecting an oxidizing blast at a low angle of incidence against thesurface of said bath in a direction from the at side of the convertertoward the curved lside thereof and across an area of said surfacearranged centrally between surface areas at the ends thereof, utilizingsaid blast to move slag continuously over said central area, circulatingthe slag in op-` posite rotational directions over the ends of saidcurved side and the said end areas of said bath to return it into thepath of the blast across said central area, and moving the gasesproduced by `said -blast with a spiral motion over the surface of thebath to said converter mouth.

UNITED STATES PATENTS Robert Ian'. 1, 1889` Murphy et al. Oct.' 11,1910Rommelaere Apr. 1, 1919 lEuler'lstein et al Oct. 14, 1941 Sims Jan. 31,1956

1. A PNEUMATIC PROCESS FOR REFINING IRON WHICH COMPRISES CHARGING A BATHOF MOLTEN IRON AND SLAG IN A CONVERTER, PROJECTING AN OXIDIZING BLAST ATA LOW ANGLE OF INCIDENCE AGAINST THE SURFACE OF SAID BATH IN A DIRECTIONACROSS AN AREA OF SAID SURFACES ARRANGED CENTRALLY BETWEEN SURFACE AREAAT THEE ENDS THEREOF, UTLIZING SAID BLAST TO MOVE SLAG OVER SAID CENTRALAREA, AND CIRCULATING THE SLAG IN OPPOSITE ROTATIONAL DIRECTIONS OVERTHE SAID END AREAS OF SAID BATH TO RETURN IT INTO THE PATH OF SAIDBLAST.